The invention relates to a control device for compressed-air brakes.
Compressed-air brakes are used, for example, in the case of rail vehicles, where the braking operation is initiated by lowering the pressure in a main air pipe. This is provided for safety reasons but means that a control device is required which ensures that, when the pressure is lowered in the main air pipe, a pressure rise takes place in the brake cylinders. Such a control device is described, for example, in European Patent Document EP 0 133 653 B1.
Because of their complexity, such control devices should have a certain size. As illustrated, for example, in Specification B-EC00.25, Picture 5 and 6, a control sleeve 101.37, a minimum pressure limiting device F and a Ü-monitor U with the Ü-chamber K are provided. These are three structural components which together represent certain constructional expenditures, particularly the position of the control sleeve in the piston rod of the triple-pressure element G influencing the size of the overall control valve. The influence is caused, on the one hand, directly by the size of the control sleeve which has an effect on the height of the housing, but also indirectly because, for operating the control sleeve and overcoming the friction of the sliding sealing caused by the control sleeve, a certain size of the diaphragm disk 101.21 is required.
The present invention provides a control device at reduced expenditures and of a smaller size. Furthermore, when automatic brakes are used, a braking of all cars which is as simultaneous and uniform as possible is to be achieved by means of the control device.
The idea on which the present invention is based is that of omitting one of three structural components as known from the prior art—the control sleeve, the minimum pressure limiting device and the Ü-monitor—without reducing functionality. The reason is that the control sleeve surprisingly becomes superfluous when the main air pipe is successfully connected in a meaningfully time-controlled manner to valve V 101.2. The control of this connection takes place by a valve whose position corresponds approximately to the minimal pressure limiting device F. An especially constructed control element is required which combines in itself the function of the Ü-monitor and of the A-monitor D of the known control device.
As a result of the present invention, the size of the control device can be reduced by approximately 50% in comparison to the known control device while the hysteresis of the device, does not exceed the normal value.
According to the present invention, the control device has a control valve in a housing. The control valve includes a piston rod with a first and second piston and a double-seat valve. Furthermore, the present invention comprises a control element, a supply air reservoir, a control chamber and a main air pipe. One side of the first piston is connected with the main air pipe in a compressed-air carrying manner, and the other side is connected with the control chamber in a compressed-air carrying manner. On one side, the second piston is connected in a compressed-air carrying manner with a brake cylinder pilot chamber or a brake cylinder, while an ambient pressure exists on the other side. The double-seat valve is connected between a compressed-air connection to the supply air reservoir and a compressed-air connection to the brake cylinder pilot chamber. The control device further includes a compressed-air connection from the main air pipe connected in parallel to the compressed-air connection from the supply air reservoir to the double-seat valve. The compressed-air connection from the main air pipe is connected to a valve that comprises a piston rod and a piston. On one side, the piston has a compressed-air connection for a control pressure and, on the other side, the piston has a device for generating a counterforce, preferably in the form of a pressure spring. The control device further includes a control element connected to the main air pipe, the control chamber, the compressed-air connection for the control pressure, the brake cylinder pilot chamber and the environment.
The second piston of the double-seat valve is connected on its second side with the environment, or ambient air, such that, in the case of a lower position of the piston rod with the two pistons, the brake cylinder pilot chamber is vented by way of the ambient air connection. In this case, in this lower position, the double-seat valve has one seat closed so that the compressed-air connection of the connection pipe from the supply air reservoir to the double-seat valve—or the pipe connected parallel thereto—is separated from the brake cylinder pilot chamber. In an upper position of the piston rod with the two pistons, the double-seat valve has one seat opened; the brake cylinder pilot chamber is separated from the environment by the second piston, so that compressed air can flow by way of the double-seat valve into the brake cylinder pilot chamber.
In an embodiment of the present invention, the double-seat valve is constructed as a tappet valve and is loaded in the closing direction by a pressure spring and in the opening direction by the piston rod of the control valve. In another embodiment of the present invention, the valve which controls the connection between the main air pipe and the double-seat valve is constructed as a tappet valve. This tappet valve can also be loaded by its pressure spring in the closing direction and in the opening direction by its piston rod.
In an embodiment of the present invention, the control element comprises a piston rod with an axial bore, a piston, a partition, a second partition and a valve. In the piston rod, a bypass is constructed for bridging the partition. On the side of the piston facing the valve, a compressed-air connection to the brake cylinder pilot chamber is constructed and, on the side of the piston facing away from the valve, a device is arranged for generating a counterforce, which device may be in the form of a pressure spring. The compressed-air connection for the control pressure can be connected by way of the valve with the main air pipe. The piston rod is arranged such that it leads from the valve through the two partitions to the piston. On the side of the partition facing the valve, a connection is constructed for the compressed-air connection with the control pressure; on the side facing away from the valve, the compressed-air connection is connected to the control chamber. The compressed-air connection to the brake cylinder pilot chamber is separated by the second partition from the compressed-air connection to the control chamber.
In an embodiment of the present invention, the effect of the pressure build-up and of the pressure reduction in the brake cylinder pilot chamber can be intensified in that a compressed-air carrying connection to another valve—for the purpose of a differentiation called a venting valve—is inserted in the connection line between the control valve and the brake cylinder pilot chamber, which venting valve opens and closes with respect to the environment. In addition, the venting valve will open up the passage to the environment when the brake cylinder pilot chamber, by way of the ambient air connection in the control valve, is vented at a lower position of the piston rod with the two pistons. The venting valve is therefore also constructed as a tappet valve. It is loaded at least indirectly in the opening direction by the control pressure and in the closing direction by a pressure spring. The venting valve may have essentially the same construction as the valve in the parallel pipe connecting the supply air reservoir and the double seat valve to the main air pipe. The venting valve may have a piston—loaded on one side by the control pressure and on the other side by a device for generating a counterforce, such as a pressure spring. The valve may also have a piston rod which, at a correspondingly high control pressure, presses open the valve that is held closed by the pressure spring thus opening up the connection of the brake cylinder pilot chamber to the environment.
An additional valve and/or a throttle or a choke may also be connected into the compressed-air connection between the supply air reservoir and the double-seat valve. Furthermore, the compressed-air connection from the main air pipe through the control element to the control chamber may be constructed to have particular pressure losses, particularly as a result of the design of the control element's bypass having a narrow flow cross-section. In addition, a valve and/or a throttle screen may be connected into the compressed-air connection between the control element and the control chamber.
Other aspects and novel features of the present invention will become apparent from the following detail description of the invention when considered in conjunction with the accompanying drawings.